Contents I. Introduction
The induction of lightning surges on overhead lines is an issue that is being investigated since long time [1]–[3]. Although the effect of earth resistivity had been disregarded in the past by some authors [3], [4], it is now recognized that it plays a relevant role on the generation of the electromagnetic fields and on the propagation of the induced surges [5]–[10]. Due to the random nature of lightning, the experimental validation of the modeling is always a difficult task, as the exact location of the lightning stroke, and a simultaneous measurement of the lightning parameters and the induced surges are hard to obtain. The most effective way to register such an event is by using rocket-triggered lightning (RTL), when the precise location of the lightning flash is known and the channel-base current can be measured. Although RTL has some differences with respect to natural lightning, after the initial stage, the properties of RTL are thought to be similar to the ones of natural downward lightning processes following the first stroke [11].
